The present invention relates to a process for producing i-brassicasterol (chemical name: 3,5-cycloergost-22-en-6.beta.-ol) which is an intermediate for producing the compound showing a phytohormone activity, and more in detail, relates to a process for producing i-brassicasterol comprising converting a mixture of natural sterols including brassicasterol into a mixture of i-sterols, and treating the thus converted mixture by the reversed-phase partition column-chromatography, thereby isolating i-brassicasterol from the mixture of i-sterols and purifying i-brassicasterol.
Recently, from the pollen of Brassica naps L., brassinolide has been found as a substance having a plant growth-promoting activity, and the chemical structure thereof has been identified (refer to Chemical and Engineering News, No. 5, page 20(1979)).
Thereafter, many brassinolide-related compounds including brassinolide itself have been synthesized, and their activity to plants has been examined. As a result, it was reported that the 24R-epimer of brassinolide had a considerable plant growth-promoting activity (refer to Org. Chem., 44, 5002(1979)) and accordingly, an industrial process for producing brassinolides having a high activity to plants has come to be demanded. Since it is necessary to obtain i-brassicasterol as the intermediate for producing the brassinolides, development of the industrially advantageous process for producing i-brassicasterol has come to be expected.
Hitherto, as a process for producing i-brassicasterol, several processes have been known, for instance, a process in which ergosterol (which is easily available as a single substance in a relatively pure state) is used as the starting material and is converted into i-brassicasterol via i-ergosterol, a process in which brassicasterol is prepared from ergosterol and the thus prepared brassicasterol is converted to i-brassicasterol and a process in which brassicasterol is separated from a phytosterol mixture containing brassicasterol and then brassicasterol is converted into i-brassicasterol.
However, in the above-mentioned process in which i-brassicasterol is derived from ergosterol, for instance, a process via i-ergosterol, the following 5 steps are necessary.
(1) tosylation, (2) hydrolysis, (3) oxydation, (4) Birch-reduction and (5) reduction by aluminum-lithium hydride (refer to Steroids 5,745 (1965)). Accordingly, such a process not only takes a long time for obtaining the object compound, i-brassicasterol, but also gives only a low yield. The process has a problem in maintenance due to the use of strongly inflammable reagent such as metallic lithium, and is not practical as an industrial process. So, the process is applicable for the preparation in only laboratory. Then, the process in which i-brassicasterol is derived from ergosterol via brassicasterol is further complicated in the steps of the procedure, and is not practical as an industrial process.
Also, in the process in which brassicasterol is separated from the mixture of phytosterols, the following five steps are necessary for separating brassicasterol itself.
(1) acetylation, (2) bromination, (3) crystallization, (4) de-bromination and (5) hydrolysis, and since the process uses highly corrosive bromine, such a process is not an industrially practicable process.
The present invention is accomplished under the above-mentioned circumstances, and an object of the invention is to provide a profitable process for isolating effectively i-brassicasterol in a pure state which is useful as an intermediate in the production of brassinolide-related compounds showing an activity on plants, from a mixture of i-sterols derived from a mixture of natural sterols including brassicasterol.